Mirror finish on metallic or plastic substrate is achieved by several traditional methods, such as electroplating, vacuum deposition and thermal evaporation. Besides of the functions of protection to the substrate and decoration of metallic feeling, the layer of mirror finish can also provide other performances or properties, such as electric or thermal conductivity. However, these traditional treatments have their own drawbacks.
Electroplating, the most commonly used surface treatment in industry, is harmful to the environment owing to large quantity of toxic byproducts and wastes. The whole process operates at high cost, owing to the complicated post-treatment procedures. This limits and blocks the further development of electroplating industry. More and more countries forbid or limit the industry of electroplating by lots of policies.
Vacuum deposition and thermal evaporation use expensive equipments, which cannot produce continuously. The batch production may make the yielding low and unstable of the product. Without other auxiliary methods to do the pre-treatment and post-treatment of the products, the performances of the coated products, especially for plastic products, by above methods may not be good enough, such as adhesion.
US20060135281 discloses a coating comprising a fine-grained metallic layer formed by electroformation (electroplating) showing a high stiffness. US20060135282 teaches a coating with small metallic material grain with size of 2 nm to 5,000 nm. A Chinese patent application, CN1944710A discloses a mirror-like coating formed by the reaction of silver nitrate solution and ammonia and sodium hydroxide. The coating is then developed by borohydride. CN101469427A teaches a silver mirror formed by spraying the solutions of silver nitrate and potassium tartrate and sodium hydroxide. The coating is post-treated by sodium sulfite.
In the above patent applications, electroplating methods are still used for the two U.S. inventions, which can not resolve the issues of high cost and environmental pollution of the wastes. Other two inventions just report the traditional mirror-like reaction of silver without special modification, which results in the poor adhesion of silver mirror-like coating and oxidation issue of the silver coating.
Consequently, there is an unmet need for a forming a mirror finish on a substrate with good adhesive property and low cost. In addition, such mirror finish can be manufactured in an effective and environmentally friendly way.